Specific glycine uptake by identified neurons of Aplysia californica. II. Biochemistry.
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Glycine is taken up twice as rapidly by neurons R3-R14 as by other identified neurons in the Aplysia parietovisceral ganglion. Earlier studies had shown that R3-R14 have much higher glycine concentrations than other Aplysia neurons. Most of the glycine taken up by R3-R14 was biochemically untransformed for at least 1 h following its uptake. Glycine is actively transported into into R3-R14 and other Aplysia neurons by carrier-mediated processes. Glycine uptake by R3-R14 was markedly reduced in the absence of Na+ and in the presence of Hg2+, while these treatments had little effect on glycine uptake by other Aplysia neurons. There appears to be a special glycine uptake system present in R3-R14 and a general glycine uptake system common to all Aplysia neurons. The elevated glycine concentrations and special glycine uptake associated with R3-R14 may indicate that glycine is utilized as a neurotransmitter by those neurons.